2F1 Recall that digital signals with more bits and/or increased sampling rate enables a more accurate representation of the analogue signal.
In the Foundation licence exam we learned that in a SDR receiver the incoming analogue signal converted into a digital signal by a device (chip) known as an ADC (analogue to digital converter). This is achieved by sampling the incoming signal into tiny pieces many times per second. Diagrams show result. Diagram shows an instance of a single sample, a small section, as a square wave. In reality the incoming RF is complex with many embedded signals and noise.
Recall that the error introduced by sampling the analogue signal to produce the digital signal is a form of distortion.
These samples are by nature in the shape of a square wave. We know that square waves have harmonics, noise, and other inter-mixed signals, but are correct for the digital mixer circuitry to analyse. However the less number of samples a second will be distorted and are not a true representation of the analogue signal from where they came.
Recall that the minimum sampling rate needs to be greater than twice the frequency of the analogue signal to adequately capture the detail of the analogue signal being sampled.
In order to overcome the distortion of the represented signal we need to increase the sampling rate. The analogue signal can represent many complex signals and noise in the received band so the samples have to be acted upon by complex mathematical functions. These are known as the Fourier Transform. This function separates the actual signals from their harmonics and noise, giving a clean capture of the required signals. Further DDC filtering cleans up the output even more before being converted back to an audio signal by the DSP and the DAC for us to hear the sounds.
Recall that the minimum sampling rate is known as the Nyquist rate.
The minimum sample rate for accuracy must be at least twice the analogue frequency that is coming in. This minimum rate is known as the Nyquist rate, named after Harry Nyquist. He discovered you need twice the given frequency to be measure accurately. Greater accuracy of the sampled signals can be made by increasing the sample rate even higher.
